I recently read an article, don't remember where, about using the dinghy as a push boat. Have you considered that? While your non-bracket is very nice looking, I think you will always see it there on the transom and it will be an eye sore, especially when you get further south and rust becomes more of a problem.
As I was sailing home from doing a bottom job last week I saw a barge pushboat that took the "form follows function" dictum to the limit. This "boat" was nothing more that a big, really big, engine with control room mounted on top. The hull was square, probably 12X12 and had two verticle push bars mounted on the front. His bow wave without a barge was impressive. So I'm thinking, how ugly is that?
Sometimes I wish "they" had never put an engine in a sailboat, but there are times when they are essential when in a narrow waterway. I like the side mount idea as it will reduce the tendency for the prop to rise out of the water as the boat pitches over wakes and waves. I think you will find it especially so on your boat which has a pretty long aft overhang, eventhought it has a low freeboard. Since you have good metal working skills I encourage you to design a really slick system that puts the outboard on the side about where the prop for an inboard would be.